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Kavitha T.,Sri Padmavathi Womens Degree and Post Graduate College | Vasantha T.,Sri Padmavathi Womens Degree and Post Graduate College | Venkatesu P.,University of Delhi | Rama Devi R.S.,Sri Padmavathi Womens Degree and Post Graduate College | Hofman T.,Warsaw University of Technology
Journal of Molecular Liquids | Year: 2014

This work presents the thermophysical properties and structure of N-methyl-2-pyrrolidone (NMP) in the binary mixtures with 1-alkyl-3-methyl imidazolium cation [amim]+ with different anions (chloride, methyl sulfate and tetrafluoroborate) of ionic liquids (ILs). A comprehensive set of properties such as densities (ρ), ultrasonic sound velocities (u) and viscosities (η) have been measured at the temperature range from 298.15 to 313.15 K over the whole concentration range of ILs under atmospheric pressure. The ILs used for the present study included 1-ethyl-3-methylimidazolium methylsulfate [Emim][MeSO4], 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF4], 1-ethyl-3-methyl imidazolium chloride [Emim][Cl] and 1-butyl-3-methylimidazolium chloride [Bmim][Cl] from imidazolium family of ILs. From these experimental data, the excess molar volume (V E), the deviation in isentropic compressibility (Δκ s) and deviation in viscosity (Δη) were calculated and adequately correlated by using the Redlich-Kister polynomial equation. The measured and calculated data were interpreted on the basis of intermolecular interactions and structural effects between like and unlike molecules upon mixing. © 2014 Elsevier B.V. Source


Vasantha T.,Sri Padmavathi Womens Degree and Post Graduate College | Attri P.,University of Delhi | Venkatesu P.,University of Delhi | Devi R.S.R.,Sri Padmavathi Womens Degree and Post Graduate College
Journal of Physical Chemistry B | Year: 2012

Protein folding/unfolding is a fascinating study in the presence of cosolvents, which protect/disrupt the native structure of protein, respectively. The structure and stability of proteins and their functional groups may be modulated by the addition of cosolvents. Ionic liquids (ILs) are finding a vast array of applications as novel cosolvents for a wide variety of biochemical processes that include protein folding. Here, the systematic and quantitative apparent transfer free energies (δ G′tr) of protein model compounds from water to ILs through solubility measurements as a function of IL concentration at 25 °C have been exploited to quantify and interpret biomolecular interactions between model compounds of glycine peptides (GPs) with ammonium based ILs. The investigated aqueous systems consist of zwitterionic glycine peptides: glycine (Gly), diglycine (Gly2), triglycine (Gly3), tetraglycine (Gly4), and cyclic glycylglycine (c(GG)) in the presence of six ILs such as diethylammonium acetate (DEAA), diethylammonium hydrogen sulfate (DEAS), triethylammonium acetate (TEAA), triethylammonium hydrogen sulfate (TEAS), triethylammonium dihydrogen phosphate (TEAP), and trimethylammonium acetate (TMAA). We have observed positive values of δ G′tr for GPs from water to ILs, indicating that interactions between ILs and GPs are unfavorable, which leads to stabilization of the structure of model protein compounds. Moreover, our experimental data δ G′tr is used to obtain transfer free energies (δ g′tr) of the peptide backbone unit (or glycyl unit) (-CH 2C=ONH-), which is the most numerous group in globular proteins, from water to IL solutions. To obtain the mechanism events of the ILs' role in enhancing the stability of the model compounds, we have further obtained m-values for GPs from solubility limits. These results explicitly elucidate that all alkyl ammonium ILs act as stabilizers for model compounds through the exclusion of ILs from model compounds of proteins and also reflect the effect of alkyl chain on the stability of protein model compounds. © 2012 American Chemical Society. Source


Vasantha T.,Sri Padmavathi Womens Degree and Post Graduate College | Kumar A.,University of Delhi | Attri P.,University of Delhi | Venkatesu P.,University of Delhi | Rama Devi R.S.,Sri Padmavathi Womens Degree and Post Graduate College
Protein and Peptide Letters | Year: 2014

In recent years, ionic liquids (ILs) represent a new class of biocompatible co-solvents for biomolecules. In this work, we report the apparent transfer free energies (ΔG′tr) for six amino acids (AA) from water to aqueous solutions of six ammonium based ILs (diethylammonium acetate (DEAA), diethylammonium sulfate (DEAS), triethyl ammonium acetate (TEAA), triethylammonium sulfate (TEAS), triethylammonium dihydrogen phosphate (TEAP), and trimethylammonium acetate (TMAA)) through solubility measurements, as a function of IL concentration at 298.15 K under atmospheric pressure. Salting-out effect was found for AA in aqueous IL solutions with increasing IL concentrations. In addition, we observed positive values of ΔG′ tr for AA from water to ILs, indicating that the interactions between ILs and AA are unfavorable. From the obtained results, we found that the selected ammonium based ILs act as stabilizers for the structure of AA. © 2014 Bentham Science Publishers. Source


Kavitha T.,Sri Padmavathi Womens Degree and Post Graduate College | Attri P.,University of Delhi | Venkatesu P.,University of Delhi | Rama Devi R.S.,Sri Padmavathi Womens Degree and Post Graduate College | Hofman T.,Warsaw University of Technology
Thermochimica Acta | Year: 2012

To address the molecular interactions between ionic liquids (ILs) such as trimethylammonium acetate [(CH 3) 3NH][CH 3COO] (TMAA), trimethylammonium hydrogen sulphate [(CH 3) 3NH][HSO 4] (TMAS), trimethylammonium dihydrogen phosphate [(CH 3) 3NH][H 2PO 4] (TMAP) and triethylammonium dihydrogen phosphate [(CH 3CH 2) 3NH][H 2PO 4] (TEAP) with N-methyl-2-pyrrolidone (NMP), density (ρ), ultrasonic sound velocity (u) and viscosity (η) measurements have been performed across the entire concentration range and the wide temperature range from 298.15 to 313.15 K in steps of 5 K under ambient pressure. Further, on the basis of the measured properties, excess volumes (V E), isentropic compressibility deviations (Δκ s) and viscosity deviations (Δη) were obtained for all these systems under the same experimental conditions. The results are correlated by the Redlich-Kister type equation. The results are also analysed on anion dependent phenomena and temperature influence on measured and derived properties of ILs with NMP mixtures. A qualitative analysis of molecular interactions between ILs and NMP is discussed in terms of the ion-dipole, ion-pair interactions, and hydrogen bonding. © 2012 Elsevier B.V. All rights reserved. Source


Vasantha T.,Sri Padmavathi Womens Degree and Post Graduate College | Attri P.,University of Delhi | Venkatesu P.,University of Delhi | Rama Devi R.S.,Sri Padmavathi Womens Degree and Post Graduate College
Journal of Chemical Thermodynamics | Year: 2012

To quantify the biomolecular interactions of protein functional groups with biocompatible ionic liquids (ILs), transfer free energies (ΔGtr′) of model compounds from water to aqueous ILs solutions have been determined from the solubility measurements, as a function of ILs concentration at T = 298.15 K under atmospheric pressure. The aqueous systems investigated contain amino acids of zwitterionic glycine peptides: glycine (Gly), diglycine (Gly 2), and cyclic glycylglycine (c(GG)) with ILs of diethylammonium acetate ([Et 2NH][CH 3COO], DEAA), triethylammonium acetate ([Et 3NH][CH 3COO], TEAA), and trimethylammonium acetate ([Me 3NH][CH 3COO], TMAA). It was found that the solubility of model compounds in aqueous IL solutions decreases with increasing IL concentration (salting-out effect). We observed positive values of ΔGtr′ for Gly, Gly 2, and c(GG) from water to ILs, indicating that the interactions between ILs and protein surface are unfavourable, which leads to stabilization of the native structure of amino acids. Moreover, our experimental data is used to determine transfer free energies (Δgtr′) of the peptide backbone unit (-CH 2CONH-) from water to IL solutions. These results explicitly elucidate that all alkyl ammonium ILs acted as stabilizers for tested model compounds through the exclusion of ILs from surface of model compounds and also reflect the effect of alkyl chain on the stability of protein model compounds. To obtain the mechanism events of the ILs role in enhancing the stability of the model compounds structure, we further studied the UV-vis spectrum analysis. © 2011 Elsevier Ltd. All rights reserved. Source

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